Method and system for pulp stock supply

ABSTRACT

A METHOD AND SYSTEM FOR SUPPLYING PULP STOCK TO A SHEET FORMING DEVICE WHICH UTILIZES A ROTARY PUMP TO ASSIST IN MIXING AND MOVING THE PULP STOCK. MEANS ARE PROVIDED FOR DIVIDING THE PULP STOCK INTO A PLURALITY OF INDIVIDUAL STREAMS AS THE STOCK LEAVES THE PUMP IMPELLER TO THEREBY DECREASE THE MAGNITUDE OF THE PRESSURE PULSES WHILE INCREASING THE FREQUENCY OF PULSES AND THEN RECOMBINING THE STOCK INTO A SINGLE STREAM FOR DELIVERY TO THE SHEET FORMING DEVICE.

T. R. CALLAHAN E' L 3,823,953

METHOD AND SYSTEM FOR PULP STOCK SUPPLY Filed. Aug. 11. 1972 2.? Sheets-Sheet I T. R. CALLAHAN ET AL 3,823,063

METHOD AND SYSTEM FOR PULP STOCK SUPPLY July 9, 1974 2 Sheets-Sheet 2 Filed Aug. 11. 1972 United States Patent 3,823,063 METHOD AND SYSTEM FOR PULP STOCK SUPPLY Thomas R. Callahan, Milford, Herbert K. Kmgsbury, S r., Cincinnati, and Thomas E. Sutton, Springdale, Ohio, assignors to Allis-Chalmers Corporation, Milwaukee,

Wis.

Filed Aug. 11, 1972, Ser. No. 279,978 Int. Cl. D21f 1/00 US. Cl. 162-212 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates in general to paper making and more particularly to a method and system for supplying pulp stock to the sheet forming device.

In the operation of paper or sheet making machines of various types, it is necessary to deliver the fiber-containing liquid stock or slurry from which the sheet is manufactured to the web forming region of the machine in the form of a wide and relatively shallow flowing stream of rectangular cross section which may or may not be under considerable pressure. Also in such machines it is desirable for economic reasons, to collect and reuse the white water (that is, the liquid that passes through the sheet forming wire). The white water is mixed with additional pulp or stock before being returned to the paper or web forming region. A practical method of accomplishing this operation is by use of a suitable pump or pumps located in the conduit system. It thus becomes necessary in the stock conduit system to transform the confined stream of liquid discharged by the pump into the shallow, relatively wide stream which is required at the web forming region.

In order to produce a sheet having uniform physical properties, the stock (which includes water, pulp, fiber, filler, dye, glue, etc.) delivered to the web forming region of the machine should be evenly distributed across the machine width. Expressed mathematically, this means that the kinetic energy and fluid pressure in unit areas of the stream delivered to the web forming region should be as uniform as possible throughout the stream cross section and, in addition, the entire stream should be maintained in a condition which is as near to steady-state flow as is possible to obtain. In other words, the stock should be delivered to the web forming region as a uniform pressure and velocity across the width of the machine and constant pressure and velocity relationship should be maintained at all times. The desirability of obtaining the uniform pres sure steady-state flow conditions described above during the operation of sheet making machines is well recognized in the paper making art and various control arrangements have been suggested and used in an effort to attain these conditions.

One particular undesirable phenomena encountered in the manufacture of paper which occurs if this steady-state condition is not maintained is a condition known as barring. Barring is the change in sheet thickness or caliper in parallel lines. These lines or barrs occur at regular intervals running across the sheet perpendicular to the direction of flow of the sheet machine. Barring is detrimental primarily because it reduces the uniformity and quality of a sheet for such subsequent operations as printing and coating.

There are a number of possible causes of barring. Since the pump is the energy source in the stock supply system, it is considered by many to be the cause of barring. Each time a pump impeller blade passes the discharge lip of the pump, a pressure impulse is transmitted to the stock slurry. These pressure pulses flow through the system in the form of a sine wave and result in high pressure pulses at the web forming device in a uniform pattern which can result in the undesirable barring effect above referred to.

To overcome this, double suction pumps with staggered impeller blades have been utilized, thereby in effect doubling the number of blade tips passing the discharge lip of the pump per revolution. This has the effect of doubling the frequency of the pressure pulsation generated each time an impeller blade tip passes the discharge lip. Also, the pump speed has increased over the years which also increases the pulsation frequency. If the volume of slurry moved is maintained constant and the pulsation frequency is increased, the magnitude of each pulse will be reduced decreasing the tendency to barr.

The manufacturers of sheet forming devices have developed machines operating at higher speeds with both horizontal or nonhorizontal wire arrangements or web forming devices. These conditions have placed greater demands on the system for uniform flow of stock while at the same time the pump manufacturer is reaching a physical limit to the number of impeller blades which may be used and speeds at which the pump may be operated. Thus a new approach is necessary in order to increase the pulsation frequency and decrease the magnitude of individual pulses.

It is, therefore, the intention and general object of this invention to provide a stock supply system wherein the magnitude of the pressure pulses caused by the system pump are reduced and their frequency is increased.

A further object of this invention is to provide a method of supplying stock to a sheet paper forming device wherein the pulsations induced by the system pump into the stock have a high frequency and a small magnitude and the pulses are generated in a pattern other than a sine wave pattern.

Another object of the invention is to provide a system for delivering stock to a web forming device of the hereinbefore described type wherein a plurality of circumferentially spaced vanes are disposed about the outer peripheral ends of the system pump impeller blades to thereby divide the output from the impeller blades into a plurality of individual streams.

A more specific object of the subject invention is to provide a system of the hereinbefore described type wherein the outer ends of the adjacent vanes are equally spaced whereas the inner ends of adjacent vanes are unequally spaced. An additional specific object of the subject invention is to provide a system of the hereinbefore described type wherein the distances between the radially outer ends of adjacent impeller blades and the radially inner ends of adjacent vanes are unequal.

These and other objects of the subject invention will become more fully apparent as the following description is read in light of the attached drawing wherein:

FIG. 1 is a schematic view of a stock supply system constructed in accordance with the invention and utilizing a Fourdrinier type machine;

FIG. 2 is a typical cross sectional view of a pump constructed in a manner for use in the system of this invention taken along the lines 1III of FIG. 3;

FIG. 3 is a partial vertical cross sectional view of a novel pump utilized in the system of this invention;

FIG. 4 is a schematic view of a modified form of novel pump which can be used in the system; and

FIG. 5 is a schematic view of a typical vaned diffuser pump which can be used in the system.

Referring to the drawing and particularly FIG. 1, a stock supply system is shown for purposes of illustration applied to a Fourdrinier type machine. The paper or web forming device includes a forming wire 6 traveling over breast roll 7. Excess white water or stock draining from the forming wire is collected in a collecting trough or wire pit 8 and flows through a pipe 9 to a circulating pump generally designated 11. A new stock supply conduit 12 is normally provided upstream from the pump 11 to make up any additional stock for the system. The resulting stock mixture is supplied through a pipe 13 to a suitable screening and/or cleaning device 14. The flow through the pipe 13 may be controlled by a number of methods such as valve 16 shown. From the screening machine the stock flows through the conduit 17 into a spreader 18 of any conventional type which spreads the stock out to equal the width of the sheet desired. From the spreader the stock is delivered through the header 19 to the discharge or slice 20 and to the web forming device.

The pump 11 shown herein for purposes of illustration is an in-line pump which can be connected directly to the system conduit. The pump inlet flange 21 may be bolted directly to one end of the conduit 9 and the pump discharge flange 22 is bolted to one end of conduit 13. Stock enters the pump pumping chamber 23 wherein it is acted upon by the impeller blades 24. The impeller blades 24 mix and pressurize the paper stock and propel it between the spaces 26 defined by adjacent vanes 27. These vanes are located about the outer peripheral edge of the impeller blades and define a plurality of passageways for the stock. The stock is caused to split into a large number of separate streams as it passes through the spaces defined by adjacent vanes. This then results in the system witnessing a large number of low magnitude pressure pulses. After the stock passes through the spaces defined by adjacent vanes, it is collected in the volute or annular chamber 28 defined by the outer peripheral ends of the vanes 27 and the pump casing. The separate streams are combined into a single stream in the volute 28 which then passes through the pump discharge into the conduit 13.

It should be noted that the spaces between the inner ends of adjacent vanes of the pump shown in FIG. 2 are unequal to one another, whether the spaces between adjacent outer ends of the diffuser vanes are equal. The unequal spacing of vanes 27 at the flow inlet area results in an uneven distribution of low magnitude pressure pulses, whereas the even spacing of vanes at the flow outlet area results in a smooth transition to singular flow in the volute or annular chamber 28.

FIG. 4 shows a modified form of pump which may be used to practice the method and system of this invention. This pump is distinguished from a typical vaned diffuser pump as shown in FIG. 5 by the spacing R and R of alternate vanes 27. These alternate vanes of different lengths provide for the formation of additional streams of stock. In the typical vaned diffuser pump shown in FIG. 5, the spacing R is constant. It is desirable to keep the spacing R at a minimum to maximize efficiency of the pump. However, it has been determined that with a minimum R distance a line of turbulence is developed in the space R. This turbulence has the tendency to produce undesirable noise.

If the spacing R is increased, the noise level is reduced, however, the efficiency of the pump is also reduced. It has been determined that by staggering the spaces R and R as shown in FIG. 4 the noise level is reduced and the higher efficiency is maintained.

With this system, it has been found that the magnitude of impulses imposed on the slurry by the pump which causes undesirable barring has been substantially eliminated. In situations where this elimination of the pressure pulses imposed by the pump overcomes the barring elfect, it is possible to eliminate or substantially reduce the size of the other components of the machine system included to overcome these pressure pulses which were previously introduced by the pump.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method of supplying stock to a sheet forming dev ce in which the stock is propelled by a rotary pump hlvll'lg a pumping chamber characterized by the steps 0 (a) delivering said stock to said pumping chamber;

(b) pressurizing and mixing said stock in said pumpmg chamber;

(c? discharging said pressurized stock from said pumping chamber at a plurality of circumferentially spaced points located about the periphery of said pumping chamber;

(d) forming a plurality of individual streams of stock;

(e) dividing said individual streams of stock into additional streams of stock;

(f) collecting said stock from said individual streams and said additional streams and combining same mtg a single stream exiting from said rotary pumps; an

(g? delivering said single stream of stock to said forming device whereby pressure pulsations are minimized.

2 The method of supplying stock to a sheet forming dev ce in which the stock is propelled by a rotary pump hwing a pumping chamber characterized by the steps 0 (a) delivering said stock to said pumping chamber;

(b) pressurizing and mixing said stock in said pumping chamber;

(c) discharging said pressurized stock from said pumping chamber at a plurality of circumferentially spaced points located about the periphery of said pumping chamber;

(d) dividing said pressurized stock into a plurality of individual streams of stock so that the initial crosssectional areas of some of said individual streams are unequal to the initial cross-sectional area of some of the other of said individual streams;

(e) forming said individual streams so that the final cross-sectional areas thereof are equal to one another;

(f) collecting said stock from said plurality of streams and combining same into a single stream exiting from said rotary pump; and

(g) delivering said single stream of stock to said forming device whereby pressure pulsations are minimized.

3. In a system for supplying stock from a source to a sheet forming device including conduit means connecting said source to said forming device, the improvement c0rnpr1s1ng:

a rotary pump connected to said conduit means in a manner to induce flow ofstock therethrough, said pump having a pumping chamber positioned to receive stock from said conduit; a multi-bladed impeller rotatably contained within said pumping chamber; vanes defining a plurality of circumferentially spaced passages positioned to receive stock from said impeller, said passages dividing said stock into a plurality of individual streams, said vanes being constructed and arranged so that the crosssectional area of the inner ends of some of said passages are une'qual to the cross-sectional area of some of the other of said passages and wherein the cross-sectional area of the outer ends of said passages References Cited UNITED STATES PATENTS 2,589,638 3/1952 Staege 162-264 X 3,156,407 11/1964 Bourquard 415l81 6 FOREIGN PATENTS 421,964 1/1935 Great Britain 415-195 S. LEON BASHORE, Primary Examiner 5 w. F. SMITH, Assistant Examiner US. Cl. X.R. 

